I read on the Hydrogen Peroxide thread that some have had success with dipping the melting zoa in a 50/50 solution of hydrogen peroxide and RODI or tank water. As for the reasons? who knows. I had a whole colony of LA lakes melt to one little nub, and thankfully after a few months it grew 2 polyps and reopened. It's now up to 4 polyps.
My darth mauls i;'ve had for about 2 years now. Started with 2 polyps, grew to 6 polyps over the next few months and then melted and the original 2 were closed for about 8 months. I just kept it in the back tank of my 120 and a few months ago they opened up again and finally a 3rd polyp.
Not sure of the science behind it, but i believe it works to kill whatever bacteria/critters are causing the zoas to melt. People seem to have more success with dipping zoas and other softies rather than sps.